There are a number of known systems containing heat-generating components which operate at different temperatures. Exemplary of this type of system are fuel cell systems which, whether stationary or vehicular, contain a number of heat-generating components requiring temperature modulation. Some heat-generating components of a typical fuel cell system include the fuel cell, the fuel generation system, auxiliary fuel cell temperature conditioners, and the traction motor in vehicle applications. Types of fuel generation systems include sodium borohydride systems, electrolyzers and fuel reformer systems. Auxiliary fuel cell temperature conditioners include humidity and temperature controls for the anode and cathode streams entering the fuel cell stack, electronics or power electronics modules, condensers, charge air coolers for cooling hot air, fuel storage systems and battery conditioners. Some of these components have different operating temperatures and therefore have different temperature modulation requirements.
In order to meet these different requirements, fuel cell systems have typically been provided with two or more independent heat transfer circuits. Each circuit has its own pumping means and heat exchange means for regulating the coolant temperature, and may have a heat transfer fluid which differs from that of the other heat transfer circuits. An example of such a fuel cell system is described in U.S. Pat. No. 5,537,956 (Rennfeld et al.), which relates to an arrangement for cooling vehicle components by use of at least two separate cooling circuits. In the Rennfeld et al. system, each circuit has its own pump and radiator/fan, with the first circuit including the fuel cell unit, and the second circuit including the electric drive motor and power controller. The two circuits are in heat exchange communication, however there is no flow communication between the two circuits.
U.S. Pat. No. 6,370,903 (Wiech) describes a heat pump type air conditioning and heating system for use in fuel cell-powered vehicles. The systems described by Wiech have two separate coolant circuits and a refrigeration circuit. The coolant circuits operate on separate pumps and are cooled by separate radiators, and may preferably be in heat exchange communication. However, there is no flow communication between the various heating and/or cooling circuits.
U.S. Pat. No. 6,360,835 to Skala describes a fuel cell powered electric vehicle having high and low temperature heat transfer circuits. The high temperature heat transfer circuit includes a heat generating fuel processor, an endothermic device, and a first circulating pump. The low temperature heat transfer circuit includes the fuel cell, traction motor, power electronics, radiator, and a second pump. The same heat transfer fluid is used in both the high and low temperature circuits. There is some flow communication between the two circuits through a pair of conduits, with the flow through each conduit being controlled by a valve.
It will be appreciated that the provision of multiple heat transfer circuits having separate plumbing, pumps and temperature modulation means greatly increases the cost, complexity and weight of a fuel cell power plant or other operating system. Thus, there is an unsatisfied need for simpler, more efficient thermal management systems.